Modulating system



H. J. M CREARY MODULATING SYSTEM Filed Feb. 7, 1930 Nov. 14, 1933.

' Inusn :1?

Harold J. I IBE'PEELP Patented Nov. 14, 1933 I UNITED STATES MODULATI'N G SYSTEM Harold J. McGi-eary, Chicago, Ill., assignor, by

mesne assignments,

to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application February 7, 1930. Serial No. 426,703

4 Claims.

The present invention relates in general to modulating systems and more particularly to the modulation of the output of an oscillator in accordance with light. The main object of the I invention is the provision of means for modulating or changing the frequency of an oscillator in accordance with the light received by a photoelectric cell.

The invention has a number of contemplated m, uses and is especially applicable to picture transmitting and television systems.

Various features of the invention will be apparent from the following detailed description and explanation of the operation of the same 5 when read in connection with the accompanying drawing comprising Figs. 1 and 2, which show by means of the usual schematic diagram two circuit arrangements according to the present invention.

In Fig. 1, 0" represents a neon tube oscillator comprising aneon tube 1 in parallel with a variable condenser 2. The oscillator is connected in series with a battery 3, a photo-electric cell i, and a high resistance 5. Output leads 6 and "I are connected to the terminals of the resistance 5.

In the modification shown in Fig. 2, the oscillator O, resistance 15, and a second resistance 18 are connected in series with the battery 13 while the photo-electric cell'l l is connected in parallel with the battery 13 and resistance 18. Output conductors 16 and 17 are connected to the ter-= minals of resistance 15.

A detailed explanation of the operation of the two arrangements shown will now be given. It is well known that a neon tube in parallel with a condenser, when connected in series with a resistance and a D. C. voltage supply, will oscillate and that the frequency of oscillation is governed by the voltage and resistance in the circuit and the capacity of the condenser shunting the tube. Normally the tube does not pass any current and the condenser is gradually charged. When the potential across the tube reaches a critical value the tube strikes and the condenser discharges. This cycle of operations is then repeated and the result is a pulsating current whose frequency may be varied by changing the voltage, resistance or capacity in the circuit.

Referring to Fig. 1 of the drawing, the resistance 5, capacity 2, and the voltage of battery 3 may be so chosen that the normal frequency of oscillation, with very little light reaching the photo-electric cell 4, is of any desired value, for example, just above the audible frequency range.

As the light reaching the cell 4 increases, theability of the cell to pass current increases and the effective resistance in the oscillator circuit decreases. This allows the condenser to charge in less time and, therefore, increases the frequency of the oscillating current in the circuit. to When the amount of light received by the cell 4 decreases, the effective resistance in the circuit increases and causes a corresponding decrease in the frequency of oscillation. The output leads 6 and '7 are connected to the terminals of the redd sistance 5 and may lead to amplifiers or as desired.

In the modification shown in Fig. 2, the photoelectric cell 14 is connected in parallel with the battery 13 and-resistance 18, Normally with little in light reaching the photo-electric cell the oscillator operates practically independently of the cell 14 and its frequency is determined by the relative values of the resistances 15 and 18, the voltage of battery 13, and the capacity of condenser J53 12. As the light reaching the photo-electric cell 14 increases, the ability of the cell to pass current increases and the increased current flow through resistance 18 reduces the potential impressed on the oscillator O. The time required to charge so the condenser accordingly increases and the frequency of oscillation decreases in. proportion.

As the light received by the cell 14 is again decreased, less current fiows through the cell and the RI drop in resistance 18 is decreased. This increases the voltage impressed on the oscillator and thereby increases the frequency of oscillation. The output leads are connected'to the terminals of resistance 15.

Having described the invention, what is thought so to be new and is desired to have protected by Letters Patent will be pointed out in the appended claims. 1

What is claimed is:

1. In combination, an oscillator comprising a neon tube, a resistance, and a battery in serial relation, a variable condenser in parallel with said neon tube, and a photo-electric cell in parallel with said battery and resistance to produce a pulsating current of varying frequency.

2. In combination, an oscillating circuit comprising a neon tube, a battery, and a first and a second resistance in serial relation, 2', variable condenser in parallel with said neon tube, output leads connected to the terminals of said first re- 1055 sistance, and a photo-electric cell in parallel with said battery and said second resistance for varying the frequency of the current in said output leads in accordance with the amount of light received by said cell. no

iii

3. In combination, a pulsating current generator comprising a resistance and a battery connected in series with a neon tube, a condenser in multiple with said tube, the tube being open to current flow when the condenser is charging and being conductive when the condenser is discharging, and a photo-electric cell connected in parallel with said resistance and said battery, whereby variations in the amount of light reaching said cell produce changes in the frequency of the pulsating current due to changes in voltage drop across said resistance.

4. In combination, a pulsating current generator comprising a neon tube, a resistance, and a HAROLD J. MCCREARY. 

